Vehicles utilizing an internal combustion engine, such as a motorcycle, have an idle configuration for phases where the engine operates but does not deliver power to the drivetrain. An engine may be idled by the operator, for example, immediately after starting the engine, while the vehicle is at rest or when the vehicle is coasting (i.e. at times when the engine is operating but is not engaged to the drivetrain of the vehicle).
Internal combustion engines operate through burning a mixture of fuel and air in a combustion chamber internal to the engine. Opening the throttle of an engine operates a valve (the “main throttle valve”) within the throttle body controlling the volume of air flowing to the engine via a main air induction passage. Fuel is either drawn into the engine or injected into the engine in response to the induction of air, and combustion of the fuel and air occurs. When the engine is engaged with the drivetrain, the combustion powers the drivetrain of the vehicle to set the vehicle in motion in response to the open throttle.
At idle, even though the throttle is closed, sufficient fuel and air must remain available to the engine for it to continue to run smoothly while delivering sufficient power to accessories such as an alternator. Without any air, the combustion would be extinguished and the engine would stop. A common design therefore provides an idle air bypass passage as an alternative ingress of air to the engine when the operator closes the throttle.
Various performance characteristics of the engine are related to the ratio of air to fuel present during the combustion. Changing this ratio may, for example, vary the smoothness of engine operation including at different phases of operation (e.g. after startup), alter a sound profile of the engine, change engine operation in response to varied external atmospheric or temperature conditions, modify engine emissions or cause the engine to have differing wear-and-tear characteristics, among other results.
The ratio of air to fuel consumed by engines in factory-built vehicles is now commonly computer-controlled, as by an Engine Control Unit (“ECU”), to deliver a target ratio of air to fuel to the engine across a variety of phases of operation, including at idle. Particularly, upon switching from carbureted engines to fuel-injected engines, at least some motorcycle manufacturers eliminated the ability for an operator to adjust idle air volume, leaving this function solely to the ECU. Prior to the foregoing change, operator control of idle air in a motorcycle was possible via screwdriver adjustment of an air mixture screw.
Now, in a common engine at idle, the ECU determines a target idle air intake volume in response to various engine operating and/or extrinsic conditions and drives a stepper motor to control an idle air control valve that opens or closes the idle air bypass passage. U.S. Pat. No. 4,337,742 to Carlson et al. discloses one such idle air control apparatus, including a stepper motor and idle air control valve in a single device designed to be controlled by an ECU.
However, some motorcycle owners and operators of newer bikes may prefer to vary the air to fuel ratio at idle themselves, even if the motorcycle includes a factory ECU and stepper motor for controlling the idle air. Even more desirable for some enthusiasts is a means of at least partially varying the idle air by hand (i.e. without a screwdriver or other tool), and while astride the motorcycle.
Accordingly, what is disclosed is an operator control system for motorcycle engine idle.